Technical Field
The present disclosure relates to a method of treating a glass surface comprising a polycarbonate using solvent immersion and chemical vapors to form a textured glass surface with a directed hierarchical patterned nanoporous structure and increased hydrophobicity.
Description of the Related Art
The “background” description provided herein is for the purpose of generally presenting the context of the disclosure. Work of the presently named inventors, to the extent it is described in this background section, as well as aspects of the description which may not otherwise qualify as prior art at the time of filing, are neither expressly or impliedly admitted as prior art against the present invention.
There has been significant recent development in photovoltaics (PVs) in order to harvest high, direct, and normal irradiation and produce energy from a renewable, clean, and sustainable source. However, climate conditions such as high temperatures and dust create many challenges. For instance, during the first eight months of a photovoltaic cell's installation in a desert environment dust accumulation takes place causing a reduction in the cell's efficiency of up to 36% due to a decrease in surface light transmittance. After 15 years of exposure to the dusty and dry environment of a desert, this efficiency reduction extends to about a 72% decrease. Therefore, photovoltaic panels installed in dry environments should be designed to minimize adhesion of dust particles over the cells' surfaces. One option for achieving this is by texturing these surfaces to have a nanopattern, such as those that mimic the Lotus leaf phenomenon [Opportunities and challenges of solar energy in Saudi Arabia. Baras, W. Bamhair, Y. AlKhoshi, M. Alodan, 2012; and Self-cleaning and antireflective packaging glass for solar modules. L. K. Verma, M. Sakhuja, J. Son, A. J. Danner, H. Yang, H. C. Zeng, C. S. Bhatia. s. l.: Renewable Energy, 2011, Vol. 36, pp. 2489-2493.—each incorporated herein by reference in its entirety].
A large number of studies have been performed to develop different techniques for the design and production of hydrophobic surfaces that mimic self-cleaning plants such as the Lotus leaf by controlling the surface topography and chemistry [S. Anand, K. Rykaczewski, S. B. Subramanyam, D. Beysens, and K. K. Varanasi, “How droplets nucleate and grow on liquids and liquid impregnated surfaces,” SoftMatter, vol. 3, no. 1, pp. 69-80, 2015; and Y. Yoon, D. Kim, and J. B. Lee, “Hierarchical micro/nano structures for super-hydrophobic surfaces and super-lyophobic surface against liquid metal,” Micro and Nano Systems Letters, vol. 2, pp. 1-18, 2014; and Y. Yoon, D.-W. Lee, and J.-B. Lee, “Fabrication of optically transparent PDMS artificial lotus leaf film using underexposed and underbaked photoresist mold,” Journal of Microelectromechanical Systems, vol. 22, no. 5, pp. 1073-1080, 2013; and B. Bhushan, Y. C. Jung, and K. Koch, “Micro-, nano- and hierarchical structures for superhydrophobicity, self-cleaning and low adhesion,” Philosophical Transactions of the Royal Society A: Mathematical, Physical and Engineering Sciences, vol. 367, no. 1894, pp. 1631-1672, 2009.—each incorporated herein by reference in its entirety]. The self-cleaning properties develop from the fact that the Lotus leaf surface has a hierarchical structure made of micro- and nanopatterns resulting in low adhesion forces of water droplets which aid in the droplet movement. Several crop plants also have the same characteristics like the Lotus leave, for example, Brassica, Alchemilla, and Lupinus [R. Wang, K. Hashimoto, A. Fujishima et al., “Light-induced amphiphilic surfaces,” Nature, vol. 388, no. 6641, pp. 431-432, 1997; and C. Neinhuis and W. Barthlott, “Characterization and distribution of water-repellent, self-cleaning plant surfaces,” Annals of Botany, vol. 79, no. 6, pp. 667-677, 1997; and T. Verho, J. T. Korhonen, L. Sainiemi et al., “Reversible switching between superhydrophobic states on a hierarchically structured surface,” Proceedings of the National Academy of Sciences of the United States of America, vol. 109, no. 26, pp. 10210-10213, 2012.—each incorporated herein by reference in its entirety]. Mimicking this nature and generating surface hydrophobicity improves the performance of photovoltaic devices by minimizing the dust accumulation at the surface which results in the degradation of the material and a significant decrease in surface light transmittance.
The design of a superhydrophobic surface requires a rough and low energy surface. An important problem of the roughness is the increase in the light reflectance from the surface and, as a result, the decrease of the surface light-transmittance. Therefore, control over the roughening of the surface should be taken into consideration. In the case of a transparent substrate, roughening of its surface often causes a reduction in the level of transparency. Thus, super-hydrophobicity and transparency are competitive properties. However, transparency can be preserved provided that the surface roughness is fine enough so as to not disturb the passage of light. This can be achieved by making the surface roughness smaller in size than the wavelength of visible light [Transparent superhydrophobic thin films with self-cleaning properties. Akira Nakajima, Kazuhito Hashimoto, Kennichi Takai, Goro Yamauchi, Akira Fujishima, and Toshiya Watanabe. S. l.: Langmuir, 2000, Vol. 16, pp. 7044-7047.—incorporated herein by reference in its entirety].
Polycarbonate glass, bisphenol A type, is one of the promising materials to be modified to develop an optimal hydrophobicity/transitivity relationship due to the versatile chemical modifications using appropriate solvents. Polycarbonate (PC) glass, one of the lowest cost materials, is used as protective covers for photovoltaic (PV) panels due to its high mechanical flexibility and low density. The surface texturing of polycarbonate glass at micro/nanoscales to generate a hydrophobic texture has been reported [Z. Fan, C. Shu, Y. Yu, V. Zaporojtchenko, and F. Faupel, “Vapor induced crystallization behavior of bisphenol-A polycarbonate,” Polymer Engineering&Science, vol. 46, no. 6, pp. 729-734, 2006; and N. Zhao, L. Weng, X. Zhang, Q. Xie, X. Zhang, and J. Xu, “A lotus-leaf-like superhydrophobic surface prepared by solvent induced crystallization,” ChemPhysChem, vol. 7, no. 4, pp. 824-827, 2006.—each incorporated herein by reference in its entirety]. The resulting hydrophobic texture enhances the non-wetting properties by increasing the trapped air between the surface texture posts. This, in turn, leads to a superhydrophobic behavior of the textured surface, since liquid droplets lay on the air pockets.
Many attempts have been carried out to generate superhydrophobic surfaces of polycarbonate glass by controlling surface morphology; however, all these approaches either are technically limited such as lithography or may result in the desired micro/nanoarchitecture but at the expense of optical properties. Among the promising solvents with suitable polycarbonate interactivity is acetone. Acetone induced crystallization has been studied intensely over the last decade; however, the fast dynamic of acetone crystallization results in the development of hierarchical spherules with high aspect ratio on the surface [E. Turska and H. Janeczek, “Liquid-induced crystallization of a bisphenol-A polycarbonate,” Polymer, vol. 20, no. 7, pp. 855-858, 1979; and S. M. Aharoni and N. S. Murthy, “Effects of solvent-induced crystallization on the amorphous phase of polycarbonate of bisphenol A,” International Journal of Polymeric Materials and Polymeric Biomaterials, vol. 42, no. 3-4, pp. 275-283, 1998; and D. Park and J.-W. Hong, “Solvent-induced crystallization and interaction parameter of the blends of bisphenol A polycarbonate and poly(phenylmethacrylate),” Polymer Journal, vol. 29, no. 12, pp. 970-974, 1997.—each incorporated herein by reference in its entirety]. This reduces the glass transmittance dramatically and hence reduces their applicability in photovoltaic panels.
De Oliveira et al. casted bisphenol A polycarbonate films with different molar masses and exposed them to an acetone vapor saturated environment for one and two days [De Oliveira, F. L. O., et al., Study on bisphenol-A polycarbonates samples crystallized by acetone vapor induction. Polymer bulletin, 2011. 67(6): p. 1045-1057.—incorporated herein by reference in its entirety]. The study demonstrated that there is a direct relationship between the polymer molar mass, the melting enthalpy, the size of the formed spherules and the degree of crystallization. This is likely a result of the presence of a high number of the repeating units. Further, Liu et al. studied the effect of polycarbonate thickness on the acetone transport kinetics within the polymer sheets [Liu, C. K., C. T. Hu, and S. Lee, Effect of compression and thickness on acetone transport in polycarbonate. Polymer Engineering & Science, 2005. 45(5): p. 687-693.—incorporated herein by reference in its entirety].
The Varanasi group made use of liquid acetone induced polycarbonated crystallization to generate superhydrophobic surfaces by immersing polycarbonate into acetone at different amounts of time [Y. Cui, A. T. Paxson, K. M. Smyth, and K. K. Varanasi, “Hierarchical polymeric textures via solvent-induced phase transformation: a single-step production of large-area superhydrophobic surfaces,” Colloids and Surfaces A: Physicochemical and Engineering Aspects, vol. 394, pp. 8-13, 2012; and Cui, Y., et al. Superhydrophobic polymer surface via solvent-induced crystallization. in Thermal and Thermomechanical Phenomena in Electronic Systems (ITherm), 2012 13th IEEE Intersociety Conference on. 2012. IEEE.; and Varanasi, K. K., et al., Hierarchical thermoplastic surface textures formed by phase transformation and methods of making. US 20120142795A1—each incorporated herein by reference in its entirety]. The group achieved a high contact angle with low contact angle hysteresis between the textured crystallized polycarbonate surface and a water droplet. The studies demonstrated that the polymeric nanofibers form secondary texture over the spherule, having a great effect on the surface hydrophobicity. The studies did not examine the effect of the texturing process on the surface transmittance. Further, a long immersion period (i.e. ˜30 min) was required to create a superhydrophobic surface, which introduces the possibility of deformation of the polycarbonate plate or the formation of powder on the surface by recrystallization of polycarbonate after solvent evaporation and the resulting significant reduction in optical properties. In addition, the research only focused on the solid liquid interface and did not refer to the use of acetone in the vapor phase.
Recently, Go et al. reported an inexpensive and facile method for fabricating nanoporous superhydrophobic polycarbonate plates by dipping them into organic solvents for a very short period of time and then modifying them with trichloromethyl silane (TCMS). The study tried different organic solvents such as CH2Cl2, methyl ethyl ketone, ethyl acetate, toluene and isopropyl alcohol [S. Go, M. Han, and Y. Ahn, “Formation of nanoporous polycarbonate surfaces and their chemical modification for superhydrophobicity,” Bulletin of the Korean Chemical Society, vol. 33, no. 11, pp. 3899-3902, 2012.—incorporated herein by reference in its entirety]. They found that only CH2Cl2 generated nanoporous structures in a short period of time (˜5 s). In their work they further silanize the surface to yield a superhydrophobic surface with a contact angle of 161°. However, the 5 s immersion in dichloromethane reduces the optical transmittance significantly.
In view of the forgoing, one object of the present disclosure is to provide a method of treating glass surfaces comprising a polycarbonate that controls the generation and growth of nanopores and spherules as well as the distance between pores to increase hydrophobicity while maintaining significant optical transmittance.